Scaling up of Indoor Air Purification Applying Photocatalytic Wall Paint

SALVADORES, FEDERICO; BERTONI, GRACIANA; DIAZ, GUILLERMINA; ALFANO, ORLANDO MARIO; BARROS, EUGENIA; BALLARI, MARÍA DE LOS MILAGROS

Praga

Conferencia; 5th European Conference on Environmental Applications of Advanced Oxidation Processes (EAAOOP5); 2017

University of Chemistry and Technology, Prague, Czech Republic (UCT Prague)

The quality of indoor air has a large impact on human´s health due to the time that people spend on indoor environments. Heterogeneous photocatalysis employing TiO2 as catalyst has proven to be an efficient method for air and water purification.In this study the photocatalytic oxidation of an indoor air pollutant, i.e. acetaldehyde, into CO2 was carry out using a developed photocatalytic paint and regular indoor lights in a bench scale photoreactor simulating a room. The reactor consists on a chamber of 50x35x30 cm3 with two entries on the top and two exits on the bottom for air inlet and outlet, respectively. The lamps are placed on the top of the reactor which is sealed with a transparent acrylic. To simulate a normal room environment, the reactor operating conditions were changed applying the D-optimal experimental design methodology. As a result of the applied experimental design, 22 different air depolluting experiments were carried out changing: the relative humidity (between 30 and 70%), air flow (0, 2.5 and 5 L/min), light irradiation level (between 5.1 and 22.7 W/m2), and pollutant concentration (2.5 and 5 ppm).The paint formulation consists of: water (30% w/w), CaCO3-extender (18% w/w), carbon doped photocatalytic TiO2-pigment (18% w/w), polymeric binder (33.5% w/w), and dispersing agent (0.5% w/w). The paint was applied with an aerograph to paper sheets and dried at ambient conditions for 24 h. After that, the paper was attached to the reactor walls and air without the pollutant was flowed for 12 h in the reactor with the lights on. This is done to degrade the non-photocatalytic compounds that surround the TiO2 particles with the aim that the photocatalyst could interact with the pollutant in the experiments.To ensure good mixing during the photoreaction, a small fan was placed in the center of the reactor. The chamber was filled with a mixture of air and acetaldehyde. After the desired concentration inside the reactor was achieved, the reactor was illuminated and the photoreaction started. Air samples were taken every 10 minutes at the outlet to follow the conversion of acetaldehyde. The samples were analyzed in a gas chromatograph with a Flame Ionization Detector (FID). The stationary state was achieved between 55 and 160 min (most of them around 120 min), and the obtained conversion of acetaldehyde varied between 3.0 and 53.0 % depending on the working conditions. On the other hand, formaldehyde is formed during the reaction; thus a total conversion was calculated taking into account the concentration of this secondary pollutant. This conversion varied between 2.9 and 46.5 %.The data analysis was done with the surface response methodology. An inverse relation between humidity and conversion, and between air flow and conversion was observed, i.e. the lower the humidity and the lower the air flow, the higher the conversion. On the other hand, the higher the radiation level, the higher the conversion. Finally, for the experiments of 2.5 and 5 ppm concentration of acetaldehyde, no significant differences in conversion were noticed. All these behaviors were observed for both the acetaldehyde and the total conversion.